A. Field of the Invention
The invention is directed to a tool for holding a magnetic directional survey instrument for inserting the instrument into a deviated well bore.
B. Prior Art
In the practice of directional drilling it is very important to determine and verify accurately the hole inclination and directional orientation of the deviated well bore. A number of companies have developed various methods and equipment to achieve these purposes.
Typical of the survey instruments available today is the magnetic multi-shot survey instrument manufactured by Scientific Drilling Controls. Their survey instrument is described and illustrated at pages 6420 and 6421 of the Composite Catalog of Oil Field Equipment and Services, 34th Ed., Vol. 4, 1980-81.
A similarly operated survey instrument is offered by Sperry-Sun and is described and illustrated on pages 6636 and 6637 of the Composite Catalog. These instruments are composed of a compass, lens, film magazine, solenoid, battery housing and batteries and often some type of electronic programmer. Also, the self-contained assembly is housed in some type of protective housing.
Typically, the survey instrument is carried or lowered into non-magnetic drill collars and the survey record taken while the drill stem is being pulled from the hole. Alternatively, the instrument may be run in an open hole on wire or other similar equipment.
With the advent of short radius curves in kicking off from vertical bore holes, it has been found that use of the above methods of hole insertion is impractical. Very often, the survey tool is damaged or rendered inoperative by the previously known methods of surveying. There has not been available a tool for housing the survey instrument which would be capable of both protecting the instrument from the downhole environment and still be capable of traversing the short radius curve.